1. Field of the Invention
The present invention relates generally to a production line arrangement and more specifically to an automated method of assembling automotive vehicles or the like.
2. Description of the Prior Art
A previously proposed production assembly arrangement used support arrangements, each equipped with a number of gauge members on which panels could be supported and clamped in position. By either moving the support arrangement to the structure under assembly such as a partially completed vehicle body, or bringing the structure to the support, the panel could be held in an appropriate position with respect to the structure, thereby facilitating spot welding of the panel to the structure.
However, this arrangement has serious drawbacks. One is that the gauge members each required hydraulic or pneumatically operated latch-like members which could be swung into position to clamp the panel (work piece) against the gauges during the welding or like operation. However, the clamping members were required to be shaped so that when they closed down on the gauge sections the resulting aperture corresponded to the cross-sectional shape of the clamped and supported panel or component. Therefore, the variety of panels and/or components which could be supported by any one support arrangement was severely limited.
Further, due to the rigidity of the panels, when the latch-like members were swung to their released positions, the panels sometimes tended to exhibit a "spring back" phenomenon or the like. As a result the panels sometimes became distorted or changed positions.
To overcome this problem it was found necessary to isolate and manually adjust the positions of the gauges that caused the "spring back" phenomena, so that when the clamping action was removed, the panels would not undergo the undesirable changes in configuration and/or position. However, these adjustments proved to be extremely time consuming and, in combination with the requirement to install and adjust new gauge members each time the line was modified (including the above mentioned type of fine adjustment), was found to badly impair the utility of the arrangement.
To overcome this problem an arrangement of the nature disclosed in JP-A-59-144595 and U.S. Pat. No. 4,691,905 issued on Sept. 8, 1987 in the name of Tamura et al, was proposed. This arrangement features the use of work piece locating devices which include gauge members which can be selectively shaped in accordance with the profile and shape of the work piece to be supported. Using these arrangements in combination with articulated robotic support devices, which permit the gauges to be moved in three dimensions, a number of panels and components can be selectively moved into predetermined positional relation with one another, and spot welded together.
However, this type of arrangement has also met with only partial success. One problem is that considerable time is required to set up the system. For instance, if the robots are provided with a control program it is necessary for an operator to "teach" each robot its procedure during the initial set up stages. This teaching involves manual control of the mechanism so that the operator actually performs the assembly operation. Once the appropriate movements are recorded, the robot is able to mimic the manually induced set of operations and thus reproduce the human activity. Accordingly, when a change in production is required, an operator must re-teach the robots in accordance with the new or modified tasks which are now required. By way of example only, should production be shifted from a sedan model to a station wagon the forward end of the vehicle will remain essentially the same. However, the rear portion will have different panels and require that the robots be taught how to manipulate the same into place and secure the same by welding. Another problem is that once in operation, this method requires constant surveillance and adjustment of the various elements to remedy any drift in their setting and prevent the assembly's accuracy from deviating outside permitted tolerances.